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Discussion Starter · #1 ·
Hello everyone,

First post!

I recently purchased a CBR125R that I knew had a few issues (learner rash, broken mirror, broken footpegs, and so on). The bike itself starts fine (it is the fuel injected model - 2007) without any stuttering or lag. Unfortunately, however, the bike revs itself up, upon starting, to about 4,000rpm and sits there for a good while. That isn't the biggest issue though. When I accelerate the revs do not snap back to zero, that is, they slowly go down until they reach the idle rpm. I have checked the spark plug, oil filter, clutch cable, and the clutch itself (making sure it wasn't sticking). The bike has been sitting for about 5 months and has approximately 30,000kms on it. I am thinking it could be something to do with the valves but I am not sure. Does anyone else have any troubleshooting advice they can offer?

Cheers!
 

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Sounds like an airleak, Is it a carb or fuel injected model?

Spray some easy start or brake cleaner around the inlet rubber and see if the revs rise
 

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Do the revs rise when you spray it or does it sit at a constant RPM?
 

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Discussion Starter · #5 ·
I'm back! The bike runs fine, goes through the gears fine but it seems to have an issue when it idles. Originally the bike wouldn't rev properly, the revs would stay high and go down extremely slowly. I fixed that issue. Now, however, the bike idles really rough and I can hear a knocking sound. This sound only appears when the bike idles, it never has any issue when you're actually riding through the gears. Sometimes, after reving the bike hard, the bike will struggle to idle and it will stall. This also happens when you're shifting down to first. I have added a video showing the rough idle below. I have done the following trying to diagnose the problem:

* Checked the throttle body for any leaks
* Checked and replaced the spark plug and cap (it was a little loose before)
* Checked the rubber thingo that sits on the inlet, no leaks
* Checked the air filter, looks new
* Checked around the throttle body/engine for any vacuum leaks, nothing
* Took the fuel tank off and emptied the fuel to make sure it wasn't contaminated
* Checked and appropriately adjusted the throttle idle screw thingo
I'm not sure what else to check, I was going to take the bike apart further and get to the vales, not sure if that is causing my issue though. Any ideas?

VIDEO:
https://vid.me/KaFQ

Thanks everyone!
 

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Have you tried putting some cleaner through the injector?
 

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Have you tried putting some cleaner through the injector?
I've pulled it all out and cleaned it already (made sure none of those small pin holes were covered/dirty).

Could there be a clutch issue? Perhaps something to do with the clutch plates? Or maybe it has something to do with improper air to fuel mixture/low compression?

I'm lost.
 

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Could be a multitude of things tbh, the noise could possibly be the clutch but to me it just sounds like a low idle on the video
 

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Discussion Starter · #9 ·
What else do you think it could be? Im going to make a list and work my way through each possible issue haha.
 

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It's hard to say without the the engine in front of you. You can't pin point these things through a video.

What i would do it listen and see if i can work out the rough area of the noise and strip and check that. Repeat the process in different areas until it's gone
 

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It's difficult to determine that problem, where it comes from. Another thing i would check was ignition timing.
 

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Have you checked the fuel line pressure? It has to be 294Kpa or 3.0kgf/cm3 (43psi). Also it would be great to check fuel filter - the problem that it is mounted inside the fuel pump. You will need to take of fuel pump and disassemble it (thanks to honda you can do it without making any damage to it), to get to the filter. Than you can wash it with kerosene if it is clogged (this filter is not selling separately so be careful). Take a look at the picture, it will tell where to search...
 

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Discussion Starter · #13 ·
I'll have to check some of these suggestions out when I'm back in the workshop. A few people have said it is a sinister engine knock. Do you think it could be? Or perhaps it is the cam tensioner or valves (but wouldn't that be making a more high pitched ticking sound)?
 

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Take the tensioner out and see if the plunger springs out fast like it should.

Sounds to me like a loose cam chain slapping when revs are low.
 

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I think that the reason of struggling at idle is lean air/fuel mixture. And if your bike has no air leak, than problem can be with fuel supply (clogged fuel injector or fuel line, dirty fuel filter, poor fuel pump performance).
 

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Discussion Starter · #16 ·
Ah, I think the little CBR is dead.

I took the bike apart again to get to the vales. I turned the engine over, ensuring that the 'T' appears near the outside edge of the disc. However, I can't adjust either valve, they spring back up. There is no room at all, the valves are completely closed. I assume something has went wrong internally...replacing the valves and getting the engine reconditioned seems like overkill for this bike. What do you guys think?
 

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So there is no available adjustment on the rocker arms?
 

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The retaining clips for the valves are still there right?

Cam lobes aren't worn badly?

May be the valve seats receeding but i've never heard of it happening on a CBR125 before
 
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